Multi-scale Waveform Tomography of the Pacific Upper Mantle Using Surface Wave Data
Date Issued
2008
Date
2008
Author(s)
Hsu, Ya-Ting
Abstract
Owing to the abundant circum-Pacific earthquakes and seismic stations, the coverage density of trans-Pacific minor-arc surface waves is highest among the globe, making the region an excellent candidate for the high resolution surface waves tomography. We invert long period waveform of Rayleigh waves in the time domain in the framework of normal-mode-based asymptotic coupling theory [Li and Romanowicz, 1995] for the upper mantle structure underneath the Pacific. In particular, we propose a two-step lateral model parameterization approach, by which both the accuracy in the forward computation and the flexibility in the inversion stage are achieved. In the first step, the initial model is parameterized in terms of spherical harmonics. Spherical harmonics can be simplified to cosine and sine functions in the great circle path connecting the source and receiver, allowing an efficient and accurate analytical solution for the path integral and therefore forward synthetics. In the second step, partial derivative matrices w.r.t. spherical harmonics are mapped onto nodes of the spherical triangle meshes within the selected region. Taking advantage of the orthogonality of spherical harmonics, the above conversion is straightforward. After the mapping, only about 10-15% of nodes receive effective sensitivities. As a result, the computation cost in the stage of inversion is significantly reduced. With the new matrices, we may utilize either the grid-based fixed-scale or the wavelet-based multi-scale inversion technique [eg. Chiao and Kuo, 2001] for the regional tomography. The new approach allows us to obtain partial derivative matrices from three different model basis for the same data set, and only one forward computation is required. We present the tomographic results, compare models derived from different model parameterizations, and discuss how the tomographic features are influenced by model parameterizations.
Subjects
waveform tomography
the Pacific upper mantle
multi-scale parameterization
spherical harmonics
NACT
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-97-R95224207-1.pdf
Size
23.53 KB
Format
Adobe PDF
Checksum
(MD5):1e5f27fb38842f6cbb6a43c6d72cb7b2